Abstract
Ancistrus Kner, 1854 is a diverse catfish genus, currently comprising 66 valid species, but karyotype data were recorded for 33 species, although only ten have their taxonomic status defined. Considerable karyotype diversity has been found within this genus, with 2n varying from 34 to 54 and structural variability including heteromorphic sex chromosomes. In many cases, uncertainty on the taxonomic status of the study populations hampers reliable interpretation of the complex chromosomal evolutionary history of the group. This study aims to present the first karyotype data for a population of the Ancistrus sp. collected in Criminoso stream (tributary of the Paraguay River Basin, Mato Grosso do Sul, Brazil) in which a combination of different chromosomal markers was used and results integrated in broad discussion on karyotype evolution in the genus. The specimens presented 2n=42 with 18m+16sm+8st and a single NOR revealed by silver nitrate and fluorescence in situ hybridization (FISH) with 18S rDNA probe, located in pair No. 10. Clusters of 5S rDNA were located in the pericentromeric region of three chromosomes: pair No. 1 (metacentric) and one of the homologues of the nucleolar pair No. 10. Heterogeneity in the molecular composition of the heterochromatin was confirmed by the association of C-banding and fluorochrome CMA3/DAPI-staining. Exploring the differential composition of constitutive heterochromatin in Ancistrus may provide an important perspective to understand genome organization and evolution within this group. Our data reinforce the chromosomal diversity present in Ancistrus genus and we discuss the potential sources these variation. The karyotype structure of Ancistrus sp. “Criminoso stream” appears to be consistent with the existence of a new candidate species.
Highlights
IntroductionAncistrus Kner, 1854 is the most species-rich genus of the tribe Ancistrini (Hypostominae), currently consisting of 66 valid species (Bifi et al 2009, Froese and Pauly 2016)
Ancistrus Kner, 1854 is the most species-rich genus of the tribe Ancistrini (Hypostominae), currently consisting of 66 valid species (Bifi et al 2009, Froese and Pauly 2016). This genus is widespread in the Neotropical region, from Panama to Rio de La Plata in Argentina, the greatest diversity of Ancistrus species is found in the basin of the Amazon River (Fisch-Muller 2003)
The Ag-nucleolus organizer regions (NOR) sites were found in the terminal position of the long arm of a submetacentric pair (No 10), which presented a clear size heteromorphism (Figure 1a, in box), confirmed by 18S rDNA-fluorescence in situ hybridization (FISH) (Figure 1b, in box)
Summary
Ancistrus Kner, 1854 is the most species-rich genus of the tribe Ancistrini (Hypostominae), currently consisting of 66 valid species (Bifi et al 2009, Froese and Pauly 2016). The karyotype data available for this genus indicate considerable chromosomal diversity, with diploid numbers ranging from 2n=34 chromosomes in Ancistrus cuiabae (Mariotto et al 2009) to 2n=54 in Ancistrus claro (Mariotto et al 2011) In addition to this numerical diversity, there is considerable variation in chromosome structure, including differences among populations that suggest the existence of species complexes, as observed in Ancistrus prope dubius (Mariotto and Miyazawa 2006). Another remarkable feature of Ancistrus is the occurrence of heteromorphic sex chromosomes in some species, including simple (Mariotto et al 2004, Alves et al 2006, Mariotto and Miyazawa 2006) and multiple systems (de Oliveira et al 2007, 2008) which has contributed to karyotype diversification within the genus
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